As the title says, fellahs, my car is raging its guts out. I tried soothing its nerves with gentle complimentary talk, but to no avail..

The horn gets stuck about 10 seconds into the drive. I can back out perfectly normal, get going and just when you think its all good, the horn kicks on. Full blast, non stop, until I turn the car off. But then restart, and she's all better. Doesn't seem related to steering, not using the signals but have turned the wiper on for a single swipe. It does it in the evenings, but not morning, if its relevant to the riddle..

Should I buy 'er flowers ?

Alarm or short circuit I reckon.

Remove the steering wheel and check the clockspring/contact ring inside. A bad setup here can cause intermittent short circuits that can result in a stuck horn. Also check that the return springs that you push against when honking the horn are all there and in the right place. If they come loose, they can either short the contacts directly or allow the contacts to "sag" against each other. All that is needed is a path to ground to activate the horn relay and sound the horn, so anything loose/worn in that assembly is trouble.

The airbag spring might be it, it feels "odd" on one of the corners, I'll get in there and inspect but I'm not even breathing on it.. and no rattles. Doesn't seem steering related, with it stuck on, I cranked lock to lock, and flexed the wheel up-down, left-right, just screaming the whole time..

Wouldn't the alarm get ticked off right away and not delay?

Could the horn have an internal short? How does the horn actually work? Any moving parts?

It always happens in the same spot, going over the same bumps, nothing else sets it off. Kinda like its allergic to that driveway or a freak magnetic field..

I got thinking (always dangerous) and the "re-start to reset" you described would only fit in you had sticky contacts on the horn relay (possible, but not likely), so that makes the clock spring less of a suspect.

On the later cars (and probably all W124s) the factory alarm uses a separate horn for the alarm alert. Are you sure it is the "fanfare" horn that is sounding and not the factory alarm horn? It is possible the factory alarm not being properly disarmed and is thus being triggered when you hit that special bump. The hood protection switch comes to mind on this.

Additionally, if you look at the attached PDF you will see that cars built prior to 07/86 (US) and 3/87 (R.O.W.) were fitted with an anti-tow feature. This was usually a spring and pendulum arrangement designed to detect when the angle of the car exceeded a predefined angle (as in, hook it up to the truck . . .). Again, if the factory alarm not being properly disarmed and your car had an early build date, the anti-tow feature may be being triggered. Just out of curiosity, do you park your car on a hill/incline?

Lastly, it is possible that the D.P.O. installed an after-market alarm - even one with an impact switch - that is wired into the fanfare horn circuit that is no longer working properly so it is being triggered when you drive.

Hope this helps.

This is probably not your problem, but your story reminds me of what happened when my son drove my car. Somehow a penny dropped into the space behind the horn cover. The horn would just start honking when you turned the wheel. Based on that experience with the penny, I'm thinking it is what others above have said. It may just be something with the contacts behind the horn cover.

Hahaha neat PDF, I particularly liked the trunk lighting may be turned off by pulling on pin, didn't know that one!

I just tested the alarm sensors, and have new hood pins so its all solid.

I don't think its alarm related, I know my horn, the one you could hear at 180mph screaming git-ah-my-wayy..

Its not hill related as I'm on flat, but it might be bumps, there's an uggly patch of cobble stone, needless to say, it shakes and rattles..

Does the relay have moving parts? How old school ! If so, engine bay temperature might be why it only does it cold.